Although detergents and cleaning compositions comprising bleaching agents are usually used in powder or granule form, there is an interest in also marketing and using such products in the liquid form.
GB Patent 1 303 810 discloses pourable, liquid compositions for cleaning and rinsing purposes which comprise a clear liquid medium and one or more particulate components suspended therein. The liquid medium, which can be aqueous or non-aqueous, comprises one or more cleaning-active components, such as anionic, nonionic or cationic surfactants directed towards the intended use. The material suspended in the liquid medium expediently comprises those components which produce a specific technical effect in the composition. Examples which are mentioned in this document are bleaching agents, enzymes and perfumes, it being possible for these substances to be surrounded by a coating which serves to avoid an interaction with the liquid medium. A cleaning composition of the generic type comprises a bleaching-active chlorine compound, that is to say a sodium hypochlorite solution, encapsulated in a polyethylene wax. The compositions of the generic type additionally comprise substances to adjust the rheological properties, as a result of which the particulate constituents are kept in a stable suspension in the liquid medium.
GB 1,303,810 A1 gives no indication of whether and in what form sodium percarbonate, which is known to be not very stable in the presence of moisture, and therefore a high loss of active oxygen must be expected during storage in a liquid detergent comprising water, can be incorporated into a liquid detergent and cleaning composition.
WO 01/66685 A1 discloses non-aqueous liquid detergent and cleaning compositions which are characterized by the presence of liquid bleaching activators. “Non-aqueous” is understood as meaning a content of free water of less than 5 wt. %, in particular less than 2 wt. %. The compositions can also comprise dispersed bleaching agents. Sodium perborates, sodium percarbonate, persulfates, peroxypyrophosphates and alkyl and aryl peroxy acids, inter alia, are mentioned. The bleaching agents can also be coated, but no specific coatings are mentioned. The compositions of the examples comprise neither sodium percarbonate nor a coated sodium percarbonate. The problem of the loss of active oxygen due to the water present during storage of such compositions comprising bleaching agents is not referred to.
WO 02/057402 A1 discloses washing- and cleaning-active liquid compositions which comprise a transparent or translucent liquid medium and solid particles, the liquid medium comprising less than 10 wt. % of water and the composition being packaged in ready-for-use portions in bags of a transparent or translucent water-soluble material. The liquid medium comprises, in particular, anionic and/or nonionic surfactants, water-soluble builders and additionally solvents, such as alcohols. The solid particles are, in particular, bleaching agents, bleaching activators and enzymes. Among the bleaching-active components, alkali metal percarbonates, in particular sodium percarbonate, are mentioned. Such substances are expediently used in granule form, and in particular in a coated form, where the coating material can include one or more inorganic salts, such as alkali metal silicates and carbonate and borate salts, or organic materials, such as waxes, oils and soaps.
An essential feature of the compositions according to WO 02/057402 A1 is that both the liquid medium and the bag are transparent or translucent. For reasons of better marketing, it has since been acknowledged that it would be more advantageous if the bag and/or the medium were opaque, since the customer could regard the suspended material as a disadvantage and/or associate it with an undesirable change in quality.
The document acknowledged above contains no example of a detergent which comprises a particulate bleaching agent, such as sodium percarbonate. The document also does not show what criteria a coating of sodium percarbonate must fulfill in order to ensure in a water-containing liquid detergent or cleaning composition on the one hand an adequate storage stability, but on the other hand a good activity during the washing or cleaning process.
It is indeed known from the abovementioned WO specification and other documents that the storage stability of sodium percarbonate in a damp warm environment can be improved by application of a single- or multilayered coating, one coating material also being an alkali metal silicate, but the products known to date have proved to be unsuitable for use in liquid detergent and cleaning compositions in one or other aspect, in particular in respect of their storage stability and release of the bleaching agent in a manner appropriate for the use.
It is indeed known that by application of a coating layer of substantially alkali metal silicate to sodium percarbonate particles the release of the sodium percarbonate in an aqueous environment can be delayed, but large amounts of coating are necessary for an adequate delay, which in their turn adversely impair the washing activity, since the alkali metal silicate is not dissolved satisfactorily in the wash liquor and the “coatings” can therefore be deposited on the laundry as grey tinge. Such undissolved constituents can also lead to undesirable deposits in the washing machine.
The doctrine of EP 0 623 553 A1 is that the dissolving time of sodium percarbonate which has a coating layer of 1.5 wt. % sodium silicate is 3.5 minutes. An increase in the coating layer to 12.5 wt. % indeed leads to a prolonging of the dissolving time to about 9 minutes, but a sodium percarbonate coated in this way proved to be unsuitable in a liquid detergent with about 5 wt. % water, because too high a loss of active oxygen occurred during storage. According to EP 0 992 575 A1 the dissolving time of sodium percarbonate can indeed be increased further by using an alkali metal silicate with a modulus of greater than 3 to 5 for the coating and employing it in a correspondingly high amount, but the products obtained in this way lead to the grey tinge already mentioned.